1. Field of the Invention
This invention relates to a drill guide assembly for a mine drilling machine and more particularly to a pair of drill guide members of the drill guide assembly that are operable to move into and out of a closed drill guide position surrounding a drill steel to maintain the drill steel axially aligned with the bore hole throughout the drilling operation.
2. Description of the Prior Art
In underground mining, it is the present practice to support the roof of a mine with roof bolts and, in certain instances, with horizontal timbers or metallic tie members secured to the surface of the roof by a plurality of roof bolts that extend through predrilled holes in the timbers or tie members. Also, it is known to substitute the metallic tie members and timbers with a rectangular roof plate that is supported in bearing relation with the roof surface when the roof bolt is fully engaged in the bore hole. A boom supported roof drill as illustrated in U.S. Pat. Nos. 3,319,727 and 3,375,880 includes boom members that support the drill pot for movement of the drill steel in a straight line as it is advanced into the rock strata. The bottom is positioned on a self-propelled vehicle that is movable to preselected locations in the mine entry for installing roof bolts in accordance with a preselected pattern that provides the optimum support of the overhead roof.
The mobile boom-type drilling machines include a linkage mechanism for moving the drill pot mounted on the front end portion of the drill boom in a vertical linear path. Means is also provided for mechanically varying the linkage to permit the drill to move in a path at an angle and in a vertical plane. In this manner, fore and aft angular adjustment for the drill steel is made and it is possible to change the angular path of the drill from a straight line vertical path to a vertical fore or aft angular path relative to the mining machine.
When the bolt holes are being drilled in relatively hard materials substantial problems are encountered in aligning the drill steel with the axis of the bore hole during the drilling operation, especially where the bolt holes are a substantial depth. It has been found extremely difficult to maintain the drill steel aligned with the bore hole throughout the entire drilling operation. When one drills in hard material, frequently the drill steel will penetrate the hard material and be deflected slightly or tilt relative to the vertical axis. Continued vertical drilling when the drill steel is tilted or deflected and not aligned with the bore hole causes the drill steel to rub against the sidewall of the bore hole, especially at a location adjacent the roof surface. Under certain circumstances, the rubbing of the drill steel on the collar of the hole causes the drill steel through friction to overheat and break. As is well known, this frictional rubbing can also cause a fire hazard at the mine face in gaseous mines. The rubbing of the drill steel against the sides of the bore hole also absorbs a substantial amount of the thrust energy imparted to the drill and reduces the drilling efficiency.
To maintain axial alignment of the drill steel with the bore hole it is the conventional practice for the operator, particularly in "spotting" the drill head to start the bore hole, to steady the drill steel with his hand. The operator continues to hold the drill steel as it advances into the mine roof to maintain the drill steel in a vertical axis for drilling a bore hole in a straight line. Thus the operator uses his hand to align the drill steel with the axis of the bore hole when the drill steel deflects and rubs against the sidewall of the bore hole. Such a practice subjects the drill operator to substantial risk of injury and should be avoided.
The following United States patents disclose a drill steel guide for centering the drill steel during starting of the bore hole: U.S. Pat. Nos. 2,350,658 2,350,659 2,350,660 2,350,661 2,365,680 2,365,681 2,365,682 2,365,683 2,365,684 2,365,685 2,365,686 2,365,687 2,394,806
These references relate generally to drill steel centralizers for a hammer type face drilling machine where the drill tool is fed along guideways of a guide toward and from the work by a feed screw. A pair of cooperating centralizer arms are mounted on the guide and include guide portions for engaging the body of the drill steel to center the drill steel during starting of the drill hole. Once the drill hole is started the guide portions are released from engagement with the drill steel.
There is need for a drill steel guide for boom type mine drilling machines to maintain the drill steel axially aligned with the bore hole and eliminate rubbing of the drill steel with the sidewall of the bore hole and thus avoid the necessity for hands-on application of the drill steel by the operator to prevent misalignment.